Field of the Invention
The present invention relates to equipment for use in drilling and finishing hydrocarbon recovery wells, to drill and tool string apparatus, to drilling methods and, more particularly, to safety mechanisms and methods for the prevention of damage due to an unintended release of a well drilling tool, drill string, tool string, or like equipment used at a wellhead site.
Discussion of the Prior Art
As is known in the art, the recovery of oil or other hydrocarbons from underground is commonly accomplished by means of a borehole, or well, which is drilled to reach a deposit. Drilling operations typically use a directional boring tool having a cutting head which incorporates drilling controls in communication with drilling controllers at the surface. The cutting head is threadedly attached to the distal end of a hollow drill rod or drill pipe which consists of various downhole components, including, for example, a bent sub for directional control, as well as an elongated string of steel drill pipe segments threadedly connected end-to-end, with each segment typically being ten (10) meters in length. Rotational motion may be imparted to the drill head by a downhole hydraulic motor or by rotating the drill string from the earth's surface to drive the boring tool with its cutting head and attached bit.
As is known, as the drill bit is rotated, a suitable drilling fluid, or mud, is pumped downwardly inside the hollow drill string and exits out of the cutting head, flowing out around the bit and upwardly in the drilled well in the annular space around the outside of the drill string to transport material loosened by the bit upwardly and out of the borehole at the well head. As the bit advances down the borehole, sections of drill pipe are added to the surface or proximal end of the drill string assembly to gradually lengthen it during the drilling.
Conventional directional drilling allows the borehole to be drilled to great depths, or to be directed downwardly and then horizontally away from the well head to reach the deposits being sought. As the well is drilled, a suitable casing is installed to preserve the integrity of the borehole. Periodically, the drill bit and cutting head are withdrawn from the borehole for servicing or to permit various tools such as surveying equipment to be inserted into the well, and in such a circumstance the sections of drill pipe are disconnected sequentially as the string is lifted out. Upon completion of the drilling and casing operation, it is often necessary to finish the well, as by perforating the well casing at the location of the hydrocarbon deposit, to allow fluid communication between the producing formation and the interior of the well casing. Perforations are usually formed using a tool or tool string incorporating a perforating gun loaded with shaped charges. The gun is lowered into the well, for example by means of a wireline, and the gun is activated to detonate the shaped charges to perforate the casing and to allow fluids to flow from the formation into the production well. Perforating guns are only one example of the downhole tools that may be inserted into the well. An example of such a perforating system is described in U.S. Pat. No. 6,779,605, which is directed to a system for controlling the activation of a downhole tool.
The installation and removal of various drilling tools in a well, or borehole, involves the use of heavy drilling tool strings suspended, for example, by wirelines or by cables which must be raised and lowered during drilling operations. The weight of such equipment poses serious safety issues, for the cable holding a tool string can break or be disconnected because of defective materials, operator error, or for other reasons. Falling tool strings not only can cause serious and costly damage to drilling equipment as well as significant delays in the drilling operation, but can cause serious injury and death to oilfield workers. For this reason, tool string housings are suspended separately from the tool strings and are frequently provided with an internal “tool trap”; that is, a mechanism to catch accidentally released tool strings to prevent them from falling.
Such internal tool traps suffer from two significant drawbacks: (1) they do not cushion the impact of a falling tool string on the trap mechanism, potentially damaging the tool, and (2) they are ineffective when the tool string is lowered below the position of the trap in the housing, as happens during inspection of the tool string. It is therefore desirable that a tool trap be designed to address these issues.
A typical contemporary drill string assembly is illustrated in U.S. Pat. No. 8,534,382 to VanPelt et al, which provides nomenclature for and illustrates the components needed to support and rotate a drill string during drilling. A number of other patents describe tools, stabilizers and control systems for protecting drill strings, including U.S. Pat. No. 3,949,150 to Mason et al, U.S. Pat. No. 6,408,948 to Fontana et al and U.S. Pat. No. 7,392,861 to Fouillou et al, all of which are incorporated herein by reference for understanding the state of the art and the relevant nomenclature.
None of the above cited references or patents, alone or in combination, address the safety issues encountered by oil field workers, particularly when a tool or a tool string is being raised and lowered by a conventional wireline, as happens during installation or inspection of the tool string.
Thus, there is an unmet need for an apparatus and a method for safely controlling drill string components during drilling operations so that when a downhole tool or tool string which is supported on a drill string, on a wireline, or on some other support mechanism is raised or withdrawn from the well, the tool supported on the distal end of the support mechanism will be prevented from falling uncontrollably if an inadvertent loss of control of the support mechanism occurs. More particularly, there is a need for a tool trap that meets the needs for safety outlined above.